/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad

Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/


#include <algorithm>
#include <cfloat>
#include <cmath>

#include "search.h"
#include "timeman.h"
#include "uci.h"

TimeManagement Time; // Our global time management object

namespace {

	enum TimeType { OptimumTime, MaxTime };

	constexpr int MoveHorizon = 50;   // Plan time management at most this many moves ahead
	constexpr double MaxRatio = 7.3;  // When in trouble, we can step over reserved time with this ratio
	constexpr double StealRatio = 0.34; // However we must not steal time from remaining moves over this ratio


									// move_importance() is a skew-logistic function based on naive statistical
									// analysis of "how many games are still undecided after n half-moves". Game
									// is considered "undecided" as long as neither side has >275cp advantage.
									// Data was extracted from the CCRL game database with some simple filtering criteria.

	double move_importance(int ply) {

		constexpr double XScale = 6.85;
		constexpr double XShift = 64.5;
		constexpr double Skew = 0.171;

		return pow((1 + exp((ply - XShift) / XScale)), -Skew) + DBL_MIN; // Ensure non-zero
	}

	template<TimeType T>
	int remaining(int myTime, int movesToGo, int ply, int slowMover) {

		constexpr double TMaxRatio = (T == OptimumTime ? 1.0 : MaxRatio);
		constexpr double TStealRatio = (T == OptimumTime ? 0.0 : StealRatio);

		double moveImportance = (move_importance(ply) * slowMover) / 100.0;
		double otherMovesImportance = 0.0;

		for (int i = 1; i < movesToGo; ++i)
			otherMovesImportance += move_importance(ply + 2 * i);

		double ratio1 = (TMaxRatio * moveImportance) / (TMaxRatio * moveImportance + otherMovesImportance);
		double ratio2 = (moveImportance + TStealRatio * otherMovesImportance) / (moveImportance + otherMovesImportance);

		return TimePoint(myTime * std::min(ratio1, ratio2)); // Intel C++ asks for an explicit cast
	}

} // namespace


  /// init() is called at the beginning of the search and calculates the allowed
  /// thinking time out of the time control and current game ply. We support four
  /// different kinds of time controls, passed in 'limits':
  ///
  ///  inc == 0 && movestogo == 0 means: x basetime  [sudden death!]
  ///  inc == 0 && movestogo != 0 means: x moves in y minutes
  ///  inc >  0 && movestogo == 0 means: x basetime + z increment
  ///  inc >  0 && movestogo != 0 means: x moves in y minutes + z increment

void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {

	TimePoint minThinkingTime = Options["Minimum Thinking Time"];
	TimePoint moveOverhead = Options["Move Overhead"];
	TimePoint slowMover = Options["Slow Mover"];
	TimePoint npmsec = Options["nodestime"];
	TimePoint hypMyTime;

	// If we have to play in 'nodes as time' mode, then convert from time
	// to nodes, and use resulting values in time management formulas.
	// WARNING: Given npms (nodes per millisecond) must be much lower then
	// the real engine speed to avoid time losses.
	if (npmsec)
	{
		if (!availableNodes) // Only once at game start
			availableNodes = npmsec * limits.time[us]; // Time is in msec

													   // Convert from milliseconds to nodes
		limits.time[us] = TimePoint(availableNodes);
		limits.inc[us] *= npmsec;
		limits.npmsec = npmsec;
	}

	startTime = limits.startTime;
	optimumTime = maximumTime = std::max(limits.time[us], minThinkingTime);

	const int maxMTG = limits.movestogo ? std::min(limits.movestogo, MoveHorizon) : MoveHorizon;

	// We calculate optimum time usage for different hypothetical "moves to go" values
	// and choose the minimum of calculated search time values. Usually the greatest
	// hypMTG gives the minimum values.
	for (int hypMTG = 1; hypMTG <= maxMTG; ++hypMTG)
	{
		// Calculate thinking time for hypothetical "moves to go"-value
		hypMyTime = limits.time[us]
			+ limits.inc[us] * (hypMTG - 1)
			- moveOverhead * (2 + std::min(hypMTG, 40));

		hypMyTime = std::max(hypMyTime, TimePoint(0));

		TimePoint t1 = minThinkingTime + remaining<OptimumTime>(hypMyTime, hypMTG, ply, slowMover);
		TimePoint t2 = minThinkingTime + remaining<MaxTime    >(hypMyTime, hypMTG, ply, slowMover);

		optimumTime = std::min(t1, optimumTime);
		maximumTime = std::min(t2, maximumTime);
	}

	if (Options["Ponder"])
		optimumTime += optimumTime / 4;
}

